1. Field of the Invention
This invention relates to method and apparatus for self-diagnosis, suitable for improving the quality of service when a malfunction occurs in a vehicle electronic control system or unit (ECU) in which a main electronic control unit (main ECU) is connected via a communication line to plural subsidiary electronic control units (sub-ECUs).
2. Related Art
As electronic control systems for vehicles have developed, the ECU used in the vehicle has become a more complicated system and now typically includes plural sub-ECUs and a main ECU governing the sub-ECUs. A conventional diagnosis system executes a diagnosis procedure (diagnosis) to detect a malfunction of an ECU under the sole control of the main ECU, so that a malfunction of any of the sub-ECUs is detected only when the malfunctioning state occurs during the time that the main ECU calls for the ECUs to diagnose malfunctions (Self-Diagnosis).
A system for conventional self-diagnosis of sub-ECUs is shown in FIG. 4. A main ECU 1 comprises a CPU 2 having a system check function and a diagnosis memory function, a memory 3 for storing diagnosis information, a clock IC 4 for generating date and time information on demand, to provide the date and time of the system check for recording in the memory, a battery 5 for back-up of the memory and the clock IC, and a communication interface 6 for data communication with sub-ECUs 10.
Each Sub-ECU 10 (10A, 10B, . . . ) comprises a CPU 11 having a self-diagnosis function, a memory 12 for storing diagnosis results obtained by the sub-ECU, and a communication interface 13 for data communication with the main ECU 1.
Referring to FIG. 5, when the system diagnoses itself, the main ECU starts a system check under direction of a service person or the like and then commands the respective sub-ECUs to start the self-diagnosis. After checking conditions of the communications with the respective sub-ECUs, the main ECU diagnoses itself. Meanwhile, each sub-ECU diagnoses itself and outputs the result of the self-diagnosis. The main ECU then sequentially receives the results of the self-diagnoses executed at the respective sub-ECUs. The main ECU displays the results of the system check done by the main ECU itself and by the respective sub-ECUs. These displayed results include those for self-diagnosis by the respective sub-ECUs and that of the main ECU and the results of the checks of the communications with the respective sub-ECUs.
FIG. 6 shows processing steps of an automatic diagnosis procedure of the main ECU. During operation of this procedure, the main ECU checks the conditions of communications with the respective sub-ECUs and executes the self-diagnosis of the main ECU itself to monitor any malfunctions in the main ECU. When no current malfunction is detected, this process is repeated in a predetermined cycle. When malfunction is detected, the malfunction details and the date and time are written in the memory with a battery for each time the malfunction occurs. The main ECU then determines whether the display of the diagnosis memory has started. If it has not started, the process returns to the beginning, and the main ECU checks the conditions of the communications linking the respective sub-ECUs. If the display has started, the main ECU calls up the diagnosis information and the date and time of occurrence of the malfunction out of the memory and displays the diagnosis memory contents. The respective sub-ECUs do nothing during this diagnosis memory function. Such a diagnosis system for an ECU is disclosed in, for example, Japanese Patent Laid-Open No. 198733/1992.
Although conventional systems can detect malfunction through the diagnoses of the respective ECUs while a current malfunction is occurring, the system cannot detect a malfunction when the malfunctioning is discontinuous, or when the malfunctioning occurs randomly. Thus, the conventional system does not have the capability of giving information of past (through the present) conditions of the respective sub-ECUs and the date and time at which a past malfunction occurred in the sub-ECUs. Because the conventional system does not provide the histories of transient malfunctions of respective sub-ECUs, it takes time to find malfunction causation and solution and the quality of servicing may suffer. Moreover, although simply applying a self-diagnosis function, such as executed by the main ECU, to the sub-ECUs will enable the sub-ECUs to achieve such a function, this expansion may create problems in that the apparatus will become bulky and costly.